1. Field of the Invention
The invention generally relates to a boost converter, and more particularly, to a boost converter utilizing coupled coils.
2. Description of the Prior Art
A boost converter is a periodically switching converter commonly used for boosting voltage and adjusting power factor in circuits. FIG. 1 is a circuit diagram of a conventional boost converter 100. The boost converter 100 includes a voltage source 110, an inductor 120, a power switch component 130, a diode 140, a capacitor 150, and a load 160. A gate terminal G of the power switch component 130 is controlled by a pulse width modulation (PWM) signal. Furthermore, a turn-on time for the power switch component 130 in a period is controlled by modulating a duty cycle of the PWM signal. When the power switch component 130 is turned on, the voltage source 110, the inductor 120, and the power switch component 130 form a closed loop, and thus current I1 flowing through the closed loop drives the inductor 120 to store energy until the power switch component 130 is turned off. When the power switch component 130 is turned off, the inductor 120 is in an energy releasing state, and thus current I2 from the inductor 120 flows to the load 160 through the diode 140. In other words, when the power switch component 130 is turned off, the inductor 120 continuously releases its stored energy. As the current I2 charges the capacitor 150, the released energy is gradually stored in the capacitor 150 and the load 160, thus achieving the goal of voltage boost. As known to those skilled in the art, the relationship between an input voltage Vi and an average value of an output voltage Vo is as follows:Vo/Vin=1/(1−D)  equation (1).
Due to excessive current and switching loss, the power switch component 130 suffers from a great deal of dissipated heat, thus degrading effectiveness and bringing the extra burden of needing to incorporate a heat dissipation mechanism. As a result, a relatively expensive power switch component capable of sustaining high stress and having low switching loss is needed herein. However, if power loss from the power switch component 130 can be distributed, the heat dissipation mechanism can be simplified or avoided, thus utilizing restricted space for circuits more efficiently. As shown in FIG. 2, another conventional boost converter 200 includes two boost conversion units 201 and 202. Currents from an alternating current (AC) voltage source 210 flow through the boost conversion units 201 and 202, and thus are rectified by rectifiers 220 respectively to form a direct current (DC) voltage. The remaining parts, including inductors 230, power switch components 240, diodes 250, capacitors 260, control circuits 270 for controlling an on/off status of the boost conversion units 201 and 202, and resistors 280, are identical to those in the boost converter 100 shown in FIG. 1. Outputs of the two boost conversion units 201 and 202 are both connected to two ends of a load 290, which means the boost conversion units 201 and 202 are connected in a parallel style. The boost conversion units 201 and 202 utilize a same control circuit as their control circuits 270 respectively. In other words, the power switch components 240 of the boost conversion units 201 and 202 are controlled by the same control signal. Therefore, the two power switch components 240 are both turned on or turned off simultaneously, and thus the two inductors 230 store or release energy simultaneously. Because of the parallel connection style, currents in the whole circuits are evenly distributed to the two boost conversion units 201 and 202, and thus heat dissipation is evenly distributed to the two power switch components 240 in FIG. 2, which differs from the situation in the boost converter 100 shown in FIG. 1.